These muddy eruptions are less deadly than actual volcanoes but also more holy.

Millions of years of oxidation make a drive down this winding Death Valley road surprisingly colorful.

An enormous natural sandstone bridge in Kentucky.

A turn-of-the-century architectural marvel built on healing mineral springs and salt licks.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

Erosion and time have created a naturally-formed water park.

One of the most scenic falls in Massachusetts has a history of death and grim legend.

These Nubian pyramids are strange and unique, even by pyramid standards.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

This hunter-gatherer architecture is believed to be the oldest religious complex known.

Native Americans built this circle of stones, which was used to predict astronomical events.

Hundreds of prehistoric stones, arranged in perfect lines in a French field.

A magically clear, blue river that seems to spring from nowhere.

This famous city eluded concrete detection until the early 2000's.

Hidden deep in the Guatemalan jungle is a turquoise paradise of natural pools, caves, and waterfalls.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

This was once the center of the Birdman cult, and is now a World Heritage Site.

The hallucinogenic center of the ancient world.

Preserved Inca city and site of the last Inca stronghold against the Spanish conquistadors.

A perfectly circular stronghold constructed in the 10th century is now a nucleus of Viking culture housing a museum, village, and reenactment of an epic Viking battle.

The largest stone moai on Rapa Nui.

Mysterious man-made rock piles form an ancient cemetery on this rocky beach in Norway.

The angel of death appears to weep black tears at this grave marker.

This ancient Irish religious site is covered in ancient carvings, many of which have barely aged.